Cast forging process for aluminum wheels

ABSTRACT

A cast forging method of manufacturing a disc for a wheel. The method may include the steps of producing a cast disc by low pressure casting, heating the cast disc to its material plasticity temperature, and placing the heated cast disc into a forging mold to forge the disc under high pressure. The method may further include the steps of inspecting the forged disc for defects, and machining the forged disc to the required end-product specifications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 60/569,787 filed May 10, 2004, hereby incorporated byreference in its entirety.

BACKGROUND OF INVENTION

a. Field of Invention

The invention relates generally to the manufacture of aluminum wheelsfor automobiles and the like, and more particularly to an improvedmethod of manufacturing aluminum wheels by forging the wheels with acasting blank instead of a raw forging.

b. Description of Related Art

Aluminum automobile wheels are typically manufactured by casting,forging or by spun-rim, flow-forming or rim rolling technology.

Existing casting technologies include, for example, gravity casting andpressure casting. Gravity casting generally involves the process ofpouring molten aluminum into a mold utilizing gravity (without anyadditional pressure) to fill the mold. This casting technique offersreasonable production costs and is acceptable for casting designs thatare more visually oriented or where weight reduction and strength is nota primary concern. Since the process relies on gravity to fill a mold,the aluminum is not as densely packed in the mold as compared to othercasting or forging processes where increased pressure is used. Due tothe limited compaction of the aluminum product, gravity cast wheelsoften have a higher weight due to the increased thickness requirementfor enabling the wheels to achieve the required strength.

In order to achieve the higher strength and lower weight requirementsdesirable for wheels, compared to the aforementioned gravity castingtechnique, pressure casting uses positive pressure to move the moltenaluminum into the mold to thus provide a denser finished product in aquicker manner as opposed to gravity casting. While the production costfor pressure casting is somewhat higher than the costs associated withgravity casting, and is typically a function of the degree of pressureassociated with the process (i.e. the higher the pressure requirement,the higher the associated machinery cost), pressure casting is generallythe most common process approved for aluminum wheels sold to the O.E.M.market or to the aftermarket.

Compared to gravity and pressure casting, for the aforementionedspun-rim, flow-forming or rim rolling technology, wheels formed by suchtechnology begin with a low pressure type of casting and use a specialmachine that spins the initial casting, heats the outer portion of thecasting and then uses steel rollers pressed against the rim area to pullthe rim to its final width and shape. The combination of the heat,pressure and spinning creates a rim area with strength similar to thatof a forged wheel, without the generally higher costs associated withforging.

Lastly, forging is the process of forcing a solid billet of aluminumbetween forging dies under an extreme amount of pressure to create afinished product that is very dense, very strong and therefore can bevery light. The traditional method of manufacturing an aluminum wheel byforging includes the steps of (i) melting, (ii) casting the melt into acylindrical blank, (iii) homogenizing of the material, (iv) extruding,(v) cutting, (vi) heating, (vii) raw forging, (viii) heating, (ix)primary forge forming, (x) heating, (xi) exact forging, (xii) removal offins, (xiii) heat treatment, (xiv) fluoroscopy inspection, and (xv)machine forming. In following these fifteen steps, it becomes readilyapparent that a great deal of time and material is expended in thetraditional forging process.

Compared to the aforementioned casting and rolling processes, the costsof tooling, development and equipment associated with forging make aforged wheel very exclusive and usually demand a significantly higherprice in the aftermarket. Further, due to the higher performancerequirements for aluminum wheels in today's market, it is also becomingreadily apparent that cast or rolled aluminum wheels cannot completelymeet all of the high performance requirements.

It would therefore be of benefit to provide a cast forging process foraluminum wheels, which is simpler in operation than the aforementionedtraditional forging process, and which provides a wheel product with thesame or better performance than wheels made from existing forgingtechnology. It would also be of benefit to provide a cast forgingprocess which is repeatable in operation, which provides a significantreduction in the overall costs associated with the manufacture of aforged wheel, and which is relatively simple to implement.

SUMMARY OF INVENTION

The invention solves the problems and overcomes the drawbacks anddeficiencies of existing cast or rolled aluminum wheel manufacturingtechnology by providing a cast forging method of manufacturing a discfor an automobile wheel and the like. The method may include the stepsof producing a cast disc by low pressure casting, heating the cast discto its material plasticity temperature, and placing the heated cast discinto a forging mold to forge the disc under high pressure. The methodmay further include the steps of inspecting the forged disc for defects,and thereafter machining the forged disc to produce a completed discwhich may be attached to a rim to product a completed wheel product, asdiscussed below.

For the method described above, the high pressure may compress theheated cast disc from approximately 5-20 mm. The low pressure mayinclude pressure of approximately 0.1-1 mpa, and the high pressure mayinclude pressure of approximately 500 mpa. The inspection may beperformed by fluoroscopy and other known techniques in the art. Themachining may include machining of the disc to its final dimensionalspecifications, and further include machining of assembly fitments, suchas hubs, valve stem holes etc. The method may further include attachingthe machined disc to a rim to form a wheel by bolts and/or welding. Thedisc may be formed of an aluminum composition, with an exemplarycomposition including elements having the following ratio:Si—approximately 6.58%, Mg—approximately 0.3%, Ti—approximately 0.2%,Sr—approximately 0.18%, L—approximately 0.2%, C—approximately 0.2%,Fe—approximately 0.16%, Al—Remainder.

Additional features, advantages, and embodiments of the invention may beset forth or apparent from consideration of the following detaileddescription, drawings, and claims. Moreover, it is to be understood thatboth the foregoing summary of the invention and the following detaileddescription are exemplary and intended to provide further explanationwithout limiting the scope of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate preferred embodiments of theinvention and together with the detail description serve to explain theprinciples of the invention. In the drawings:

FIG. 1 is a flow chart of the manufacturing steps for a related forgingprocess;

FIG. 2 is an illustration of the various processes associated with thecast forging manufacturing method of the present invention;

FIGS. 3 a-e are various illustrations of the forged disc according tothe present invention being connected to a spun rim; FIG. 3 c being anillustrative cutout view of the disc and rim assembly being connected bybolts; and

FIG. 4 is an illustration of the manufacturing steps for the castforging manufacturing method of the present invention, including theprocess from casting blank to raw forging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings wherein like reference characters refer tolike and corresponding parts throughout the several views, FIGS. 2-4illustrate various manufacturing steps and schematics for the castforging process according to the present invention.

Specifically, referring to FIG. 1, a traditional method of manufacturingan aluminum wheel by forging may include the steps of (i) melting at 10,(ii) casting the melt into a cylindrical blank at 12, (iii) homogenizingof the material at 14, (iv) extruding at 16, (v) cutting at 18, (vi)heating at 20, (vii) raw forging at 22, (viii) heating at 24, (ix)primary forge forming at 26, (x) heating at 28, (xi) exact forging at30, (xii) removal of fins at 32, (xiii) heat treatment at 34, (xiv)fluoroscopy inspection at 36, and (xv) machine forming at 38.

Generally, the present invention aims to simplify and incorporate theaforementioned first eight steps (i-viii) of manufacturing an aluminumwheel, and directly uses the casting blank to heat and forge.Thereafter, the forged wheel may be machined to reach the product sizespecifications. Based upon testing performed herein, it has been shownthat the cast forged wheel produced by the cast forging process of thepresent invention includes mechanical properties superior to those oftraditionally cast or forged wheels.

Specifically, referring to FIG. 2, the present invention cast forgingprocess may first use low pressure casting to produce a cast disc 40with a partial rim 42. The low pressure casting may be performed usingair pressure field technology with an air pressure range ofapproximately 0-0.1 mpa (0-1 kg/cm²) as shown at 43. Upon completion ofthe low pressure casting step, cast disc 40 may then be heated to itsplasticity temperature as shown at 44, which is the temperature at whichthe aluminum material becomes plastically distorted, as is known in theart. Once at the plasticity temperature, cast disc 40 may then be placedinto a forging mold 45, where the heated disc is forged under highpressure into the exact desired shape. A screw pressure machine (notshown) capable of approximately 8000 tons of pressure may be used toforge cast disc 40 under high pressure. Depending on the structural andperformance requirements of the wheel, the amount of compression for thehigh pressure step may vary from 5-20 mm as shown at X in FIG. 4.Compared to the aforementioned low pressure casting which uses airpressure of approximately 0.1-1 mpa, the high pressure casting may usethe aforementioned screw press to product a piston pressure ofapproximately 500 mpa. After a predetermined time interval to enable thecast disc to solidify, forged disc 46 may be removed from the mold withthe forging press rod.

Forged disc 46 may then be inspected for inner defects usingfluoroscopy, which involves the use of X-rays to carry out theinspection of the forged disc, as is known in the art. It should benoted that other inspection techniques known in the art may be used forinspection of the forged disc, without departing from the scope of thepresent invention.

If no inner defects are found in forged disc 46, the disc may be heattreated according to its material properties to improve its machiningproperties. Thereafter, the heat treated disc may be machined to therequired wheel size specifications. The machining may include machiningof assembly fitments such as the hub, valve hole and bead seat, whiletaking into account parameters such as offset, pitch circle diameter toautomobile and tire installation requirements.

In order to form a completed wheel, a wheel rim 48 may be formed byconventional spinning stroke rotary formation, which involves thespinning of an aluminum plate in a spinning stroke rotary formationmold. It should be apparent that other methods may be used for rimformation without departing from the scope of the present invention. Forexample, an aluminum tube may be simply cut off to form the rim, or analuminum plate may be rolled and then welded to form a rim.

Referring next to FIGS. 3 a-e, once the spun wheel rim 48 is formed,forged disc 46 and spun wheel rim 48 may be connected together by bolts50 for ensuring balanced performance for the wheel assembly, as is knownin the art (see FIGS. 3 a-c). It should be noted that other methodsknown in the art may be used for connecting disc 46 to rim 48, as wouldbe apparent to those skilled in the art. For example, disc 46 may beconnected to rim 48 by welding and the like, which would provide a yetfurther lighter wheel product. In addition to the bolts, the forged discand spun wheel rim may be bonded together by using a conventionalsealing gum (i.e. an hermitic glue at 49) for preventing leakage of airbetween the disc and the rim upon tire installation. Once assembly ofwheel 52 is completed, the wheel may be inspected as shown in FIG. 3(d),and thereafter prepared for delivery as shown in FIG. 3(e).

In order to meet the performance criterion for forged wheels, thealuminum material used for the cast forging process of the presentinvention may use a special chemical composition for facilitating thecasting process and for enabling the finished wheel product to meet therequired forging performance. The alloy material may be composed ofAl—Si—Mg and other elements in the following ratio (Si—6.58%, Mg—0.3%,Ti—0.2%, Sr—0.18%, L—0.2%, C—0.2%, Cu 0.0%, Sb-0.0%, Fe—0.16%,Al—Remainder). By using this composition of material, a wheel productproduced by the cast forging process of the present invention is able tomeet and/or exceed the strength, weight and performance requirements oftoday's forged wheels.

Based upon the cast forging process discussed above, the forged aluminumwheel of the present invention also provides several distinct benefitsover wheels formed by conventional casting, rolling or forgingtechniques. For example, compared to the traditional forging processwhich requires the manufacturing steps of (i) melting, (ii) casting themelt into a cylindrical blank, (iii) homogenizing of the material, (iv)extruding, (v) cutting, (vi) heating, (vii) raw forging, (viii) heating,(ix) primary forge forming, (x) heating, (xi) exact forging, (xii)removal of fins, (xiii) heat treatment, (xiv) fluoroscopy inspection,and (xv) machine forming, the cast forging process of the presentinvention eliminates several of the aforementioned manufacturing steps,which results in a significant reduction in the machining time, increasein metal material usage, and reduction in the overall manufacturing andend-product cost by as much as 40%. Since the present invention uses thecasting blank as the raw material for forging, this use providesunlimited design freedom for the disc. Because of the use of theAl—Si—Mg composition of the present invention in combination with thecast forging process disclosed herein, the invention provides animproved wheel product having fewer defects, such as pin holes and thelike. Further, because of the use of the Al—Si—Mg composition of thepresent invention in combination with the cast forging process disclosedherein, the aluminum wheel product can achieve up to 10% elongation evenin the region of the hub and have a tensile strength of up to 250 N/mm²,thus providing a superior wheel product as required for today'sautomobiles.

As discussed throughout the description, various modifications may bemade to the cast forging steps discussed above, without departing fromthe scope of the present invention. For example, while the forged discis described as including a partial rim and being attached to a spunrim, it is conceivable that the forged disc may be produced with orwithout a partial rim for enabling attachment to a rim. Additionally,while the present invention describes a method of producing a castforged disc, those skilled in the art would readily appreciate in viewof this disclosure that the present invention manufacturing process isnot restricted to use with a wheel disc, but may be used with anyconceivable product which may be forged.

Although particular embodiments of the invention have been described indetail herein with reference to the accompanying drawings, it is to beunderstood that the invention is not limited to those particularembodiments, and that various changes and modifications may be effectedtherein by one skilled in the art without departing from the scope orspirit of the invention as defined in the appended claims.

1. A cast forging method of manufacturing a disc for a wheel, saidmethod comprising: producing a cast disc by low pressure casting;heating said cast disc to its material plasticity temperature; placingsaid heated cast disc into a forging mold to forge said disc under highpressure to produce a forged disc; inspecting said forged disc fordefects; and machining said forged disc.
 2. A method according to claim1, wherein said high pressure compressing said heated cast disc fromapproximately 5-20 mm.
 3. A method according to claim 1, wherein saidlow pressure including pressure of approximately 0.1-1 mpa, and saidhigh pressure including pressure of approximately 500 mpa.
 4. A methodaccording to claim 1, wherein said inspection being performed byfluoroscopy.
 5. A method according to claim 1, wherein said machiningincluding machining of assembly fitments.
 6. A method according to claim1, further comprising attaching said machined disc to a rim to form thewheel.
 7. A method according to claim 6, wherein said machined discbeing attached to said rim by one of bolts and welding.
 8. A methodaccording to claim 1, wherein said disc being formed of an aluminumcomposition.
 9. A method according to claim 8, wherein said aluminumcomposition including elements having the following ratio:Si—approximately 6.58%, Mg—approximately 0.3%, Ti—approximately 0.2%,Sr—approximately 0.18%, L—approximately 0.2%, C—approximately 0.2%,Fe—approximately 0.16%, Al—Remainder.
 10. A wheel disc formed by themethod of claim
 1. 11. A cast forging method of manufacturing a disc fora wheel, said method comprising: producing a cast disc by low pressurecasting; heating said cast disc to its material plasticity temperature;and placing said heated cast disc into a forging mold to forge said discunder high pressure to produce a forged disc.
 12. A method according toclaim 11, further comprising: inspecting said forged disc for defects;and machining said forged disc.
 13. A method according to claim 11,wherein said high pressure compressing said heated cast disc fromapproximately 5-20 mm.
 14. A method according to claim 11, wherein saidlow pressure including pressure of approximately 0.1-1 mpa, and saidhigh pressure including pressure of approximately 500 mpa.
 15. A methodaccording to claim 12, wherein said inspection being performed byfluoroscopy.
 16. A method according to claim 12, wherein said machiningincluding machining of assembly fitments.
 17. A method according toclaim 12, further comprising attaching said machined disc to a rim toform the wheel.
 18. A method according to claim 17, wherein saidmachined disc being attached to said rim by one of bolts and welding.19. A method according to claim 11, wherein said disc being formed of analuminum composition.
 20. A method according to claim 19, wherein saidaluminum composition including elements having the following ratio:Si—approximately 6.58%, Mg—approximately 0.3%, Ti—approximately 0.2%,Sr—approximately 0.18%, L—approximately 0.2%, C—approximately 0.2%,Fe—approximately 0.16%, Al—Remainder.